System effectiveness simulator and computer



April 9, 1968 E. J. ALTHAUS ETAL 3,377,471

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SIMULATOR AND COMPUTER SYSTEM EFFECTIVENESS l8 Sheets-Sheet 1 8 Filed July 21, 1964 mWN Fl w United States Patent 3,377,471 SYSTEM EFFECTIVENESS SIMULATOR AND COMPUTER Edward J. Althaus, Playa Del Rey, Edward P. Andert,

Anaheim, and Ernest M. Richter, Fullerton, Calif., as-

signors to Hughes Aircraft Company, Culver City,

Calif., a corporation of Delaware Filed July 21, 1964, Ser. No. 384,176 13 Claims. (Cl. 235-152) This invention relates generally to devices for demonstration and analyzing the time related and population size related properties of populations of entities subject to stochastic transformations from one state to another, and also the statistical behavior of queues or waiting lines. This invention relates particularly to a reliability simulater for accurately relating variable statistical reliability and maintainability quantities to system effectiveness and availability.

In units such as specific electronic equipment, devices or systems, the interactions between logistic and maintenance operations and reliability of the equipment pr0- vides problems which must be solved in order to determine parameters such as replacement rates, checkout efficiency and mission effectiveness or success probability. For example, in a population of systems, which may be aircraft, spacecraft, missiles or submarines, it is desirable to know the effectiveness or the availability of units which are subject to the incidence of both detected and undetected failures with repairs being continuously or periodically performed on failed systems. Frequently, statistical reliability and maintainability problems have been solved by mathematical manipulations programmed in a digital computer using tabulated random or otherwise distributed numbers. However, the necessity of providing a problematical expression for digital computers which faithfully represents the stochastic process and the need for controlling distribution values are factors that can be avoided by a device such as here described which instead of utilizing formulas, incorporates the actual occurrence of random events. Examples of statistical problems that are difiicult to solve on conventional computers or analytically are those that include non-steady processes, such as during population growth, breakdown of the repair depot and the occurrence of simultaneous events. Also, all tht computer results are not often available for continuous visible monitoring which may be desirable where population conditions are to be studied by trial and error insertion of initial or intermediate conditions, for example.

Some types of probability problems are solved as a function of a Poisson exponential distribution and some as a function of a geometric distribution in which a random event must happen, if the event occurs, at the end of a fixed interval of time. For example, repair events may occur either at fixed intervals, with a Poisson random distribution or with a geometric distribution. A simulator that would provide selection of sources of events of either fixed occurrences or of a desired type of random occurrence or of a desired type of random occurrence would be highly desirable and useful in the art.

It is therefore an object of this invention to provide a machine operable to perform a highly representative reliability simulation.

It is a further object of this invention to provide a system reating statistical theory to visible hardware for rapidly solving statistical problems in a manner that provides a hitherto unavailable verification of mathematical simulation through the action of actual statistical procedures.

It is a still further object of this invention to provide a system that solves problems of system or unit availability and reliability with an improved and simplified arrangement for developing random events.

It is another object of this invention to provide a stochastic simulator in which the results of continuous probability determinations may be continuously monibored and observed.

It is still another object of this invention to provide a statistical reliability simulator system in which populatons may be varied and in which at least one of the sources of events may be selected to provide desired distributions of the occurrence of events.

It is another object of this invention to provide a reliability simulator system having sources of random events that are controllable to provide variable average rates of occurrence.

It is another object of this invention to provide a reliability sinluator having a system time scale that is readily related to real time and in which a variable system time scale is provided.

It is another object of this invention to provide a system for forming waiting queues.

Briefly, the reliability and maintainability simulator in accordance with the principles of the invention may simulate the conditions of a complex of systems with a population of up to 30 systems, for example. The number of elements in the population is only limited by physical size of the machine. Each element which simulates a system is subjected to random failures which may remain undetected or detected as a function of the specific capabilities of the checkout equipment being simulated. Failure events are produced by random pulses generated by a radioactive source to provide a random or Poisson distribution of pulse in time. Each system is maintained or repaired at a single repair depot and the system element enters the repair depot upon the occurrence of a detectable failure. The repair rates and failure rates may be adjustable for any simulated complex of systems but is fixed for each system element and identical at the rate selected for the complex of systems.

The source of repair pulses may be a random or Poisson distribution pulse source, a source providing a geometric distribution (repair at the end of fixed intervals) or a fixed repair rate. Undetected failures in any system are identified by a display device but do not cause the initiation of a maintenance period. The simulator system .provides displays for visual demonstrations of the population in operable condition, in a failed but undetected COndition and in the repair or waiting condition. The average failure rate is variable for selecting favorable time parameters relative to real time. The average repair rate is adjustable over a wide range during either random repair or repair after fixed intervals.

Each system element is simulated by two flip flops having states 1 through 4 simulating four system element conditions which are respectively normal operate, undetected failure, detected failure and repair. An element is normally in the operate condition and remains in that state until a random failure pulse changes the element to either states 2 or 3 (undetected or detected failures), The percent of detected failures over the undetected failures is variable over a wide range for the system complex. System elements are turned in for repair upon occurrence of a detected failure state in response to sequentially sampling of each element with the output signal of a first ring counter. When a system or a plurality of systems have a detectable failure or are in the repair depot, an identified system responds to generation of repair pulses. A second shift register is provided to identify a system in repair or having a detected failure and hold until that particular system element is repaired and changed to state 1. Systems in repair lose their identity and may be repaired out of the order in which they entered but provide an average repair time. A bidirectional counter maintains a count of the number of elements in repair and controls yellow indicator lights displaying a waiting queue of elements in repair. Green and red indicator lights respectively representing specific elements in operate and undetected failure states are provided to provide a continuous display of the changing results of probability problems.

The novel features of this invention, as Well as the invention itself, both as to its organization and method of operation, will best be understood from the accompanying description taken in connection with the accompanying drawings in which like characters refer to like parts, and in which:

FIG. I is a schematic block diagram showing the overall functional operation of the system in accordance with the invention;

FIG. 2 is a schematic block diagram of the reliability simulator system in accordance with the principles of the invention;

FIG. 3 is a schematic block and circuit diagram of a typical simulated system element utilized in the simulator system of FIG. 2',

FIG. 4 is a table showing the states of the two flip flops utilized in the system elements such as the typical system element of FIG. 3;

FIG. 5 is a list of logical equations for explaining the term breakdown of the logic of the element of FIG. 3;

FIG. 6 is a schematic circuit and block diagram of the random or Poisson pulse source utilized as the failure pulse generator of FIG. 2;

FIG. 7 is an elevation view of the adjustable rate radioactive source utilized in the random pulse source of FIG. 6;

FIG. 8 is a schematic circuit diagram for further explaining the pulse source of FIG. 6;

FIG. 9 is a schematic circuit and block diagram of the control and synchronizing circuits utilized in the failure pulse generator of FIG. 2;

FIG. 10 is a schematic circuit diagram of the variable width square Wave pulse generator utilized in the portion of the failure pulse source shown in FIG. 9;

FIG. 11 is a schematic block and circuit diagram of the repair pulse source utilized in the reliability simulator of FIG. 2-,

FIG. 12 is a schematic circuit and block diagram of the repair pulse synchronizing circuit utilized in the repair pulse source of FIG. 11;

FIG. 13 is a schematic circuit diagram of the variable rate relaxation oscillator utilized in the repair pulse source of FIG. 11;

FIG. 14 is a schematic circuit and block diagram of the E register and logical gates utilized in the system of FIG. 2;

FIG. 15 is a schematic circuit and block diagram of the M register and logical gates utilized in the system of FIG. 2;

FIG. 16 is a schematic circuit and block diagram of the reset source utilized in the reliability simulator of FIG. 2;

FIG. 17 is a schematic circuit and block diagram of the signal source for registering all or any number of systems initially in the repair or Waiting condition utilized in the simulator of FIG. 2;

FIG. 18 is a schematic circuit diagram of a portion f the system element population control switch that may be utilized in the simulator of FIG. 2;

FIG. 19 is a schematic circuit and block diagram of the bidirectional counter utilized in the simulator of FIG. 2 for maintaining count of the number of elements being repaired;

FIG. 20 is a table for explaining the control of the yellow repair lights by the bidirectional counter in the system of FIG. 2;

FIG. 21 is a schematic circuit and block diagram of the display logic for the green and red indicator lights utilized in the system of FIG. 2;

FIG. 22 is a schematic circuit diagram for further explaining the control of the yellow repair lights by the bidirectional counter in the system of FIG. 2;

FIG. 23 is a front view of the display panel showing the arrangement of the lights in the system of FIG. 2 for monitoring and observing the solutions to statistical problems;

FIG. 24 is a front view of the display panel utilized in the system of FIG. 2 showing the clock and the counters for detected and undetected failure events, repair events and source counts;

FIG. 25 is a schematic circuit and block diagram of a typical counter utilized in the display panel of FIG. 24;

FIG. 26 is a schematic circuit diagram of a typical flip flop with negative and gates that may be utilized in the system of FIG. 2 when negative and or nand" logic is utilized in accordance with the principles of the invention;

FIG. 27 is a schematic circuit diagram of a typical negative and gate that may be utilized in the system of FIG. 2 in accordance with the principles of the invention;

FIG. 28 is a schematic diagram of voltage waveforms as a function of time for further explaining the failure pulse generator utilized in the simulator of FIG. 2;

FIG. 29 is a schematic diagram of additional voltage waveforms as a function of time for explaining the operation of the failure pulse generator of FIG. 2;

FIG. 30 is a schematic diagram of waveforms for explaining the operation of the three selectable sources of repair pulses utilized in the Source of repair pulses of FIG. 2; and

FIG. 31 is a schematic diagram of voltage waveforms as a function of time for explaining the operation of the repair pulse synchronizing circuit of FIG. 12.

Referring first to the functional diagram of FIG. 1, the simulator in one arrangement in accordance with the invention simulates a complex of systems or units with a population that is selected up to 30 systems, for example. The simulated systems may be any of a plurality of types of systems such as ground-based, fixed or mobile weapons, satellites, automobiles or any type of system or unit that is subject to failure which may be detected and may be repaired at a predetermined or random repair rate. As problems in maintainability can be proportionally reduced in time scale, the time of simulated operations which may be in seconds, minutes and hours can be related to real time which may be in years. The simulator system may during initiation of a reliability simulation problem operate with all simulated systems being energized which may be 30 system elements, for example, or may operate with a selected number of those system elements. Each system element stores states 1 through 4 which respectively simulate any operating condition, an undetected failure condition, a detected failure condition and a repair condition. A clock is initiated at the start of the operation. Each of the system elements is then subjected to random detected failures and to random undetected failures which mathematically both have a Poisson probability distribu tion, that is, a distribution which is proportional to ewhere A is the inverse of the mean time to failure or is the average failure rate. Failures are provided by a geiger counter tube responding to the random decay of a mass of radioactive atoms, that is, a certain average fraction of the surviving atoms decay in each time interval and produce radiation such as gamma rays. The radium salts used have a decay half life of hundreds of years and thus the average rate is essentially constant. Each operating system in the block 10 then effectively moves to a block 12 when an undetected failure event occurs and to a block 14 representing state 3 upon the occurrence of a detected failure. System elements in the block 12 which have an undetected failure are also equally subjectto detected failure pulses along with system elements in the block 10 so that the system elements with undetected failures are also subject to random failures to move to the block 14. 

1. A DEVICE FOR SIMULATING STOCHASTIC EVENTS OF A PLURALITY OF SYSTEMS COMPRISING A PLURALITY OF ELEMENTS, EACH ELEMENT INCLUDING A FIRST AND SECOND FLIP FLOPS, EACH ELEMENT SIMULATING A DIFFERENT ONE OF THE PLURALITY OF SYSTEMS AND HAVING STATES REPRESENTATIVE OF THE OCCURRENCE OF FIRST EVENTS AND OF SECOND EVENTS, A SOURCE OF FIRST EVENT PULSES RANDOM IN TIME AND COUPLED TO SAID PLURALITY OF ELEMENTS, A SOURCE OF SECOND EVENT PULSES COUPLED TO SAID PLURALITY OF ELEMENTS, AND CONTROL MEANS COUPLED TO SAID PLURALITY OF ELEMENTS FOR CONTROLLING SAID ELEMENTS TO BE SEQUENTIALLY AND REPETITIVELY ENERGIZED TO BE RESPONSIVE TO THE OCCURRENCE OF SAID FIRST EVENT PULSES AND TO BE SEQUENTIALLY SELECTED WHEN IN SAID STATE REPRESENTATIVE OF THE OCCURRENCE OF SAID FIRST EVENT TO BE RESPONSIVE TO SAID SECOND EVENT PULSES. 